In forthcoming 5G networks, slicing has been proposed as a means to partition a shared physical network infrastructure into different self-contained logical parts (slices), which are set up to satisfy certain requirements. Although the topic has been thoroughly investigated by the scientific community and the industry, there are not many works addressing the challenges that appear when trying to exploit slicing techniques over WiFi networks. In this paper, we propose a novel method of allocating resources for WiFi networks to satisfy minimum bit rate requirements. We formulate an optimization problem, and we propose a solution based on the theory of Lyapunov drift optimization. The validity of the proposed solution is assessed by means of a simulation-based evaluation in Matlab.